The invention relates to materials suitable for use in low cost, mass sensitive NOx sensors and methods for making such materials. The invention relates also to NOx sensors incorporating such materials and which can be used, for example, in mobile diesel and lean burn gasoline engines.
Legislative standards are tightening the allowable NOx emissions levels from vehicles using mobile diesel and lean burn gasoline engines. In view of the stricter standards, it would be advantageous to monitor and control emissions for compliance, e.g., using on-board diagnostics. Indeed, proposed On Board Diagnostics (ODD) regulations would require automakers to manufacture vehicles with real-time NOx monitoring, which could lead to improved engine performance, reduced emissions and substantial cost savings. One approach to optimizing performance and reducing emissions is to supply accurate ammonia dosing based on real-time NO and NO2 measurements. The various applications of NO, sensors, however, pose a challenge to engine manufacturers and sensor OEMs due to different requirements in terms of sensitivity, detection speed, and durability.
Commercial NOx sensors are known. In a typical commercial system, the principle of operation involves converting NO and NO2 into oxygen, and detecting the change in oxygen content via permeation through an oxygen membrane such as a yttria-stabilized zirconia (YSZ) membrane. However, conventional commercial systems are relatively large and expensive and tend to exhibit shortcomings with respect to durability, sensitivity, particularly at low ppm levels, and selectivity (e.g., the ability to differentiate between NOx and NH3).
In view of the foregoing, it would be advantageous to develop a low cost NOx sensor platform, including a NOx sensing material having improved durability, sensitivity and selectivity over conventional systems and materials.
These and other aspects and advantages of the invention can be achieved using a mesoporous, transition metal oxide NOx sensing material having a basic surface character and high surface area. The mesoporous transition metal oxide comprises one or more of yttrium oxide, lanthanum oxide and cerium oxide, and can be prepared using a surfactant-templated self-assembly process.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description present embodiments of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the invention and together with the description serve to explain the principles and operations of the invention.